Recovery of Reference Clock on a Device

1. A method for recovering a device reference clock on a device, the device reference clock proportional to a host reference clock of a host, when clock signaling from the host to the device is unavailable, wherein the device is configured to communicate to the host, the method comprising: measuring a ratio between the host reference clock and the device reference clock of the device by monitoring, with the device, host start-of-frame markers communicated from the host to the device; creating a recovered reference clock based on the measured ratio; and creating local start-of-frame markers at the device that are phase locked with the host start-of-frame markers based on the recovered reference clock.

2. The method of claim 1 , further comprising tracking a microframe local to the device based on the recovered reference clock.

3. The method of claim 1 , further comprising generating an audio reference clock local to the device based on the recovered reference clock.

4. The method of claim 3 , further comprising generating one or more audio sample rates based on the recovered reference clock.

5. The method of claim 3 , further comprising generating information for an asynchronous feedback endpoint based on the recovered reference clock.

6. The method of claim 3 , further comprising performing synchronous sample rate conversion based on the recovered reference clock.

7. The method of claim 3 , further comprising performing asynchronous sample rate conversion based on the recovered reference clock.

8. The method of claim 1 , wherein the host is a Universal Serial Bus host and the device is a Universal Serial Bus device.

9. The method of claim 1 , wherein creating the recovered reference clock based on the measured ratio comprises: detecting a phase difference between the host start-of-frame markers and a recovered reference rate; filtering the phase difference to generate a filtered phase difference; and comparing the filtered phase difference to the device reference clock to generate the recovered reference clock.

10. The method of claim 1 , wherein creating the recovered reference clock based on the measured ratio comprises: detecting a phase difference between the host start-of-frame markers and the recovered reference clock; filtering the phase difference to generate a filtered phase difference; and comparing the filtered phase difference to the device reference clock to generate the recovered reference clock.

11. A device, comprising: an input for receiving information communicated from a host to the device; and a controller configured to recover a device reference clock on the device, the device reference clock proportional to a host reference clock of the host, when clock signaling from the host to the device is unavailable, wherein the device is configured to communicate to the host, by: measuring a ratio between the host reference clock and the device reference clock of the device by monitoring, with the device, host start-of-frame markers communicated from the host to the device; creating a recovered reference clock based on the measured ratio; and creating local start-of-frame markers at the device that are phase locked with the host start-of-frame markers based on the recovered reference clock.

12. The device of claim 11 , the controller further configured to track a microframe local to the device based on the recovered reference clock.

13. The device of claim 11 , the controller further configured to generate an audio reference clock local to the device based on the recovered reference clock.

14. The device of claim 13 , the controller further configured to generate one or more audio sample rates based on the recovered reference clock.

15. The device of claim 13 , the controller further configured to generate information for an asynchronous feedback endpoint based on the recovered reference clock.

16. The device of claim 13 , the controller further configured to perform synchronous sample rate conversion based on the recovered reference clock.

17. The device of claim 13 , the controller further configured to perform asynchronous sample rate conversion based on the recovered reference clock.

18. The device of claim 11 , wherein the host is a Universal Serial Bus host and the device is a Universal Serial Bus device.

19. The device of claim 11 , wherein creating the recovered reference clock based on the measured ratio comprises: detecting a phase difference between the host start-of-frame markers and a recovered reference rate; filtering the phase difference to generate a filtered phase difference; and comparing the filtered phase difference to the device reference clock to generate the recovered reference clock.

20. The device of claim 11 , wherein creating the recovered reference clock based on the measured ratio comprises: detecting a phase difference between the host start-of-frame markers and the recovered reference clock; filtering the phase difference to generate a filtered phase difference; and comparing the filtered phase difference to the device reference clock to generate the recovered reference clock.